Conventionally, a decoration light-string is made by connecting, in series or in parallel, sockets of bulbs with wire conductors. In addition, the light-string can be inserted into a translucent plastic tube so as to form a tube light. However, the tube light made in this way is comparatively expensive, and connecting the bulbs with the wire is also time consuming. Furthermore, the work of pulling the light strings into the light tubes is not easy, which may also destroy the bulbs. When the bulbs are burned out, replacement of the bulbs becomes difficult. Also, the bulbs inside of the tube may not be moved or relocated, nor can the number of bulbs be increased or decreased. One prior example is the "Socket Structure of Decoration Lights" disclosed in Taiwanese Utility Model Patent No. 29873, which comprises bulbs, sockets, contacts and a holder. The sockets are disposed above the wires, and slots are provided in the sockets. The contacts are inserted into the slots and then go through the sockets, and are finally secured to the core of the wires. The holder is provided underneath the wires, where both sides of the holders extend upward so as to fasten tightly on the sockets, thereby securing the sockets on the wires.